Is a total overhaul possible in, say, 12 hours?

Well, no. You can’t seriously drop pounds, lose inches or sculpt muscles in just one day. But you can use the following quick-fix tactics to look better and bolster your confidence.1. Put in a little extra oomph in your cardio.
Just for today, do 10 extra minutes of cardio at about 10 percent above your typical workout intensity. While this won’t affect the short-term poundage picture all that much, you’ll burn more calories than usual and you’ll feel better about yourself. Bonus: High intensity exercise, combined with lovey-dovey emotions, should minimize your appetite.

2. Perk up your posture.
Good posture makes you appear 10 pounds thinner than you actually are. For a longer, leaner look in an instant, try this Wall Roll-Up:

Stand with your back against a wall and your feet a comfortable distance from the wall, heels together and toes apart. Pull your abs in, and gently press your entire back, including your neck and shoulders, into the wall. Let your arms hang down at your sides, loose and relaxed.
Drop your chin to your chest, and then peel your neck off the wall, followed by your shoulders, then your upper back, then your middle back, and then your lower back. Keep your tailbone and your butt against the wall. Hang forward a moment and then slowly reverse the movement, pasting your entire spine back onto the wall until you have returned to the starting position.
3. Pump up pre-date.
Right before your date, do a couple sets of push-ups and biceps curls. This will pump blood into your muscles, making them appear more buffed and toned than they actually are. The special effects should last for an hour or two. Trust me, this works. Men have been using this trick for centuries.